"It's been 3 ½ months, and we don't know any more now than we did in the beginning," said Velma Jacobs, Kari Bowerman's grandmother.

Bowerman, 27, of Lake Geneva, died unexpectedly in Vietnam, and her family still doesn't know why.

The brief autopsy report explaining Bowerman's death hardly gives her family comfort. They claim Vietnam's government is covering up what really killed her in the interest of protecting the country's successful tourism industry.

WISC-TV found that more than half a dozen other tourists' recent deaths are similar to Bowerman's, including her own travel partner. Some Asian media reports suggest the tourists were poisoned by a chemical meant to kill bed bugs.

"Kari and I had been friends since the age of 14. We met (during our) freshman year of high school," said Jason Von Seth, Bowerman's longtime friend.

The last time the two met was in July when Von Seth took pictures of them in South Korea.

"She kind of looked into the program, and she jumped on board and absolutely loved it," Von Seth said about the two times Bowerman spent teaching English in Seoul.

It's when Bowerman and fellow teacher Cathy Huynh took a break this summer and traveled to Vietnam that things went wrong, Bowerman's family said.

"They spent time on the beach. They went to dinner. They went and had a few drinks after dinner. They went back to their hotel, and they woke up in the morning sick," Jacobs said.

Both women left their hotel on the Nha Trang coast for a local hospital. Huynh was treated and released from the hospital, but Bowerman wasn't. Three hours after being admitted, Bowerman died.

"The hotel won't talk. The hospital won't talk. The police won't talk -- nobody will talk," said Jacobs, whose frustration is compounded by the couple of sentences in an autopsy report recently released to Vietnam's U.S. Consulate from local police suggesting Bowerman died from respiratory failure and brain swelling.

"It does, ultimately, get absorbed and metabolize where you could do an autopsy a few days later, and you may not be able to find evidence that was in the patient's body," Martin said.

Martin said chemical poisoning symptoms are similar to other sicknesses and that if diagnosed quickly, someone who has been poisoned can be treated.

Asian media outlets are linking Bowerman's death to other tourists who died in Thailand.

Washington state native Jill St. Onge and a Norwegian woman stayed in the same hotel when they visited the country three years ago.

Two years later, New Zealander Sarah Carter would go there, followed by Noemi and Audrey Belanger a year later. Thai police reportedly found an insect repellent meant for crops and bed bugs in the Canadian sisters' bodies. That insect repellent is banned in most countries, but it's legal in Thailand and Vietnam.

The cases have caught the attention of travel expert Peter Greenberg.

"The patterns here are quite similar," Greenberg said. "People are staying in hotels that have used these chemicals. We don't know the extent to which these chemicals were used, but that seems to be the common thread."

The mysterious trend doesn't stop with Bowerman's death. Despite leaving the hospital, her co-worker, Huyhn, died two days later.

As for the investigation, the World Health Organization told CNN that it suspects poison in the deaths but can't trace its origin.

"I guess for me, personally, I'm just wondering if another situation like this is going to occur and how many more situations like this have to occur before somebody does something about it," Von Seth said.